Cascaded emitter followers are often used as buffers in integrated circuit (IC) amplifiers. Such a cascade provides close to unity voltage gain which means that the power gain, current gain and output to input isolation are related to the number of stages and the current gain of each stage. For example, a two stage cascade will have a current gain of approximately Beta squared where Beta is the transistor current gain. Thus, since a typical IC transistor has a Beta of about 200, the two stage cascade has a current gain of 40,000 and a three stage cascade 8,000,000. The impedance of the output load appears at the input multiplied by the same values. Such isolation is useful in coupling a high voltage gain amplifier to a low impedance load.
Unfortunately, such cascades, while quite stable for resistive loads, can be unstable when driving capacitive loads. Under a severe capacitive load, the cascaded emitter followers can produce ringing in response to input transients. In an extreme case, the circuit can oscillate.